I. We previously demonstrated that the toxins alpha-sarcin, ricin, Shiga toxin and Shiga-like toxin all inactivate protein synthesis in cells by attacking a highly conserved region near the 3-end of 28S ribosomal RNA and that microinjection of modified deoxyoligonucleotides, ribonucleotides and ribozymes complementary to the same region of 28S RNA also abolish protein synthesis. Surprisingly, a variety of nucleases are as effective as these toxins at abolishing protein synthesis. While most nucleases hydrolyze all cellular RN, one of these nucleases selectively hydrolyzes tRNA, but not ribosomal or mRNAs, when injected into Xenopus oocytes. II. During early development Xenopus replicates its DNA nearly as fast as E. coli in log phase. We demonstrated that oocytes are an excellent source of DNA repair activity. Pyrimidine dimer repair was shown by microinjecting UV-irradiated plasmid DNA into oocytes or adding damaged DNA to an extract derived from oocytes. We have also studied DNA repair for alkylated and chemically modified DNA as well as DNA replication with our repair extract.